Re: snowman on burner pipe

Dastgir:

Little confusion. Alkai dust should have moved to inlet rather than outlet with air momentum.

Hello Gulam,

Alkalis are not completely evaporated in the burning zone. The very hot clinker passing under the burner pipe and falling into the first pasrt of the cooler is still giving off volatile alkalis into the secondary air in the vicinity of the burner pipe. There is enough in some cases to make the dust flowing around the burner pipe 'sticky'. I have chemically tested material from these rhino horns and found it to be composed principally of high alite clinker dust with elevated K2O.(~2%)

Additional evidence that there are still quite significant amounts of volatile alkalis in this area is given by the fact that high chrome steel in the nose ring of the kiln is often attacked severely in the presence of oxygen to form bright yellow alkali chromates, which migrate into the kiln bricks around the nose ring and cause them to also become bright yellow near the shell. Such chromates are formed by the action of alkalis and oxygen on chromium in the steel;- eg

              2 Cr  +  3 O2  +  2 K2O   --->   2  K2CrO 4

Dastgir:

Moreover, why reducing conditions in kiln cause dusty kiln conditions. May be FeO does not favour melt formation. Am i right?

It is not the reducing conditions that are causing the dusty kiln, it is the damage or misalignment of the burner pipe by the weight of the rhino horn that may result in poor combustion and CO in the back end.

Regards,

Ted.

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Re: snowman on burner pipe

Dear Ted,

My second question was generic one. Whether or not rhino horns build up, whenever kiln become dusty, to possibilities are raised -

1. Diminished alumina ratio

and

2. Reducing conditions in kiln. 

I want to get something substantial behind the second reason.

Regards,

Gulam Dastgir

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Re: snowman on burner pipe

Dastgir:

My second question was generic one. Whether or not rhino horns build up, whenever kiln become dusty, to possibilities are raised -

1. Diminished alumina ratio

and

2. Reducing conditions in kiln. 

I want to get something substantial behind the second reason.

Okay,

I guess it's possible for reducing conditions to effect the dustiness of clinker, but I don't think it's a significant cause. Dusty clinker is the result of problems with clinker nodulisation in the burning zone... either too little liquid phase, low surface tension and viscosity of the liquid phase, excessive or insufficent burning zone temperatures,  too little residence time of the clinker, or coarse or inhomogenous raw meal.

I think the reason there is a lot of misconception about reducing conditions causing clinker dustiness is because both are often associated with high SO3... but are related to high SO3 in different parts of the kiln.

High SO3 in the kiln inlet is the result of poor burning (reducing) conditions whereas high SO3 in the raw materials/fuel will tend to cause low surface tension of the liquid phase, resulting in poor nodulisation and dusty clinker.

So, putting it simply, high SO3 in the kiln inlet (SO3 recirculation due to reducing conditions) does not necessarily mean that the SO3 content of the liquid phase is also high. It is the final amount of SO3 in the liquid phase that matters.

Regards,

Ted.

References:-

Peter C. Hewlett, "Lea's Chemistry of Cement and Concrete",  4th Edition, pp. 164-165.

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Re: snowman on burner pipe

It may not be dust. If the burner protrudes into the kiln, the reason may very well be that sticky materials (e.g. still contain some liquid phase) are lifted to the top of the kiln and drop onto the burner tip. This is easy to determine by visual inspection.

Lumpy coating near the burner tip or even shark teeth can work as an "elevator" carrying the material to the top of the kiln.

Rhinos often have a very bad impact on kiln operation. They affect the distribution of secondary air, and the flame will suffer. Usually you'll see the NOx go down, and in the worst cases you get locally reduced conditions.

If the problem is caused by material dropping onto the burner, the radical solution is to withdraw the burner and align the tip with the kiln outlet, but if the materials are sticky, you will probably just get snowmen in the cooler instead. Another try is to move the burning zone further up the kiln to increase the length of the cooling zone inside the kiln or (if possible) change the raw mix composition.

Some shoot the rhinos with water (high pressure), but that will eventually destroy the protective casting of the burner. It is much better to mount an airgun with a protected pipe on top of the burner and the nozzle just before the rhino "foothold".

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